delta call为什么这里是大于0？

NO.PZ2023091802000145 问题如下 A bank hsolUS300,000 of call options on 100,000 equities. The equities tra 50, the option strike priis 49, the maturity is in three months, volatility is 20%, anthe interest rate is 5%. How es the bank lta-hee? A.Buy 65,000 shares. B.Buy 100,000 shares. C.Buy 21,000 shares. Sell 100,000 shares. This is at-the-money option with a lta of about 0.5. Sinthebank solcalls, it nee to lta-hee buying the shares. With a lta of0.54, it woulneeto buy approximately 50,000 shares. Answer A is theclosest. Note thmost other information is superfluous. 请问能提供一下计算lta的过程么？

NO.PZ2023091802000145 问题如下 A bank hsolUS300,000 of call options on 100,000 equities. The equities tra 50, the option strike priis 49, the maturity is in three months, volatility is 20%, anthe interest rate is 5%. How es the bank lta-hee? A.Buy 65,000 shares. B.Buy 100,000 shares. C.Buy 21,000 shares. Sell 100,000 shares. This is at-the-money option with a lta of about 0.5. Sinthebank solcalls, it nee to lta-hee buying the shares. With a lta of0.54, it woulneeto buy approximately 50,000 shares. Answer A is theclosest. Note thmost other information is superfluous. 此题如果按照公式ns=-nc*lta,ns=-300000*0.54=162000,解析中nc代入的是100000，为什么？